Protection of electric systems



Feb. 7, 1928. 1,658,704

M. D. CAMHY PROTECTION OF ELECTRIC SYSTEMS Filed March 11, 1926 A I vvv v v v v v p V l/ l v v v v v l A A A A A A i 3 AVAVAVA AVA V v v v v v I V Inventor: MusaFFeP Daub Camh His Abtorneg- Patented Feb. 7, 19

UNITED PROTECTIGE' GE ELECTRIC SYN Application filed March 11, 1926, Serial l lo. 9492?, and in 5 My invention relates to improvements in the protection of electric systems and more particularly to improvements in the protection of apparatus for generating polyphase alternating currents and has for an object to provide an improved protective arrangement for protecting polyphase generators on the occurrence of internal faults.

For protective purposes, electric systems are often provided with diiferential protective devices or over-current protective devices or both. The differential protective devices are arranged to operate when an abnormal condition such as a short-circuit occurs within the zone or portion of the svs tem which is protected. Generally. the differential protective devices operate quickly enough to open circuit the part of the system to be protected before damage is done. With electric current generators. a fault such as a short-circuit mav occur on the generator side of the circuit interrupter which connects the generator to the system either in the generator itself or the corn nectine leads therefrom. The operation of the differential protective devices to open the circuit interrupter is. however. partiallv ineffective since the current supply is not interrupted at the short-circuit point. The field weakening which occurs simultaneous- 1y certainly tends to diminish the do x and the short-circuit current is reduced as a result of decreasing! the potential. The cur rent, however, remains so high that on further running of the genera o the windino's thereof may sustain considerable damae'e. Thus, with the usual connection. the yenerator protective devices. although the isolate the faulty genera-tor from the svstem and thereby prevent other generators working in parallel from feeding into the fault are not entirelv efficacious. If the faultv generator itself is to he protected against the effect of its own fault. then a generation of currentin it must he made impossible.

In accordance with my invention. this generation of current is prevented on the operation of the protective device in that not only the switch between the generator and the circuitis released but also another switch which interconnects the phases of the windings is substantially simultaneously released so that the windings are in contact only at the fault point. lVhen faults occur on the s vsten: beyond the switch L interrupte wh h the to the em. 1 switches rele ments for arr:

hfy in from the fol. nection with and its sco pended cl in the drawing a protective M wi l he poin:

., ins;

vention. 1. herein to shown as a one end or ach 0 l use circuit is; 9 and i enter 1 211' EXCltQi? 14: and a discharge resistance 8O normally to he short circi through the contact: f; 17.

in order that the wind'ir'. 3 he disconnected not only rot :e o but also from each other. t .e other enc of each of these windings hrought out through leads 18. 19 and 20 respectively which are arrano'ed to he A terconnected hy switch circuit interrupter 21 having a no trip coil 22. In the ill ated einhodinient of in -J invention. the sent is such to provide connec on. the neutral point 23 of which may or may not be grounded. on

For controlli and 21 a fault.

svstem the generator .eans ich that. for a fault ice or t the switch 11 is on ie generator both td 1 are opened. This erential protective s n plurallief:

Q6 and S, 9, 10 and L. m and 20 res.

c. r o velv and having their secondaries connec in series normallv for circulating current. The secondary or ciroi the circulating current circuits:

culating'current circuits may have in series therewith the respective current windings 30, 31, 32 of a polyphasepower directional relay 33 whose potentiol coils 3e, 35, 36 are arranged to be energized from the bus 5, 6, 7

example; through the auxiliary relay 17,

their contacts being arranged in parallel so that upon the operation of any one, the relay 1? is energized to complete the circuit of the trip coil 12 and close contact in the circuit of the trip coil 22. Across equipotential points of the secondary circuits are connected over-current relays 4L1, 42 43 which are consequently energized in a cordance with therespectivc differences between the currents in the corresponding leads from the ends of the respective windings, that is the diiierence between the currents flowing at the points where the current transformers areconnectedr F or a fault on the system beyond the switch 11,. excess current will appear in one or more of the circulating current circuits and consesuently one or more of the relays 38, 39, 40 will operate thereby ei iecting the energization of the auxiliary relay 1?. This relay iii-turn completes the circuit of the trip coil 12 of the switch 11, cuts in the dis char ge resistance 15 and closes contacts in the circuit of thetrip coil 22. Since the currents in. corresponding leads "or conductors at the points where the current transformers are located are the same underth'e faultcondition assumednone. oithe relays ll, 4-2 4-3 will operate'and herefore the circuit of the trip coil 22willnotbe completed. Consequently only the switch 11 will be opened.

For a fault within the tone between the 7 generator 1, power may be fed into'the fault from the system thereby causing the power directional relay to operate or son e ne of the overcurrent relays 38, 39 40 may operate due-to excess current in one or more quently, the auxiliary relay 17 is energized. This relay completes the circuit of trip coil 12, closes contacts int-he circuit of trip coil 1 outs in the di charge re, r f the fault condition assumed. the currents in corresponding conductors atthe points where the current transformers are located are no longer equal and the e cease to have the same poten ial. Therefore, at least one of the relays 41, 42 48 is enerl potential polnts. 1n the secondary circuit sized and closes its contacts thereby coni Cerise v onta-c t remains only at the fault ierefore, the circulation of current 7 r e windings is prevented.

hat I claim as new anddesire to secure letters Patent of the United States, is as ollo-rsz i i 1. combination with a polyphase erator', a switch for interconnecting the crater windings at one end thereo; and means for effecting the opening, of said switch on the occurrence of abnormal conditions on the 'enerator windings. a

2. in combination with a polyphase' electric circuit a polyphase generator, circuit interruptingnica-ns for contracting-Hie generator windin to the circuit and for-in terconnectiug the windings, and. relay means operative on the occi .rence of fault on the generator windings to control the int-or:- rupting means.

gen-

In combination with a threephase ndings in staiyand differential pro"- E crate-r a for controlling the switch on J: A i

he occurence o crgized t en the currents in the leads windings.

in combination witlra pol phase cl'ec triccii'cuit and a: pelypbase generator I edit interrupter for c one e. l' oi? each of the o; 7 windings to the cur" from one ct and relay m for he ci interrupter a d the l nged to open" only the circuit ii he occurrence of a fault on the open both the circuit interi switch on the occurrence of a V uerator windings;

e '6: combination with a three-phase gen;

c t r. a switch ror connecting; the generator i, on the occurrence of a fault on nerator windings. v witness whereof, I have hereunto set hand this 9 rd day of Februe 1926.

Muse nanr Carri-Ir.

in accordance with'the diif'eren ce b'el and i tective1neansconii eff cting the opening of rc'onnecting the other V 

